1. Field of the Invention
The present invention relates to display devices. More particularly, the present invention relates to a light-blocking layer which prevents ambient light from being reflected on a reflective surface of an electrode formed in the display devices.
2. Description of the Related Technology
A plasma display panel (PDP) device is one kind of flat panel display, and recently, it has competed with LCDs or projection TVs and its market has rapidly expanded.
A PDP device typically includes a front substrate with a transparent electrode (sustain electrode) and a bus electrode, and a rear substrate with a cell structure including an address electrode, a dielectric layer, a barrier rib, and a fluorescent layer.
A voltage is applied between the electrodes of both substrates to cause electric discharge in the cell and generate ultraviolet rays. The ultraviolet rays in a cell excite a fluorescent material, and thus luminescence occurs. An image which is formed by a combination of red, green, and blue (RGB) cells of a luminescent panel is displayed on the front substrate.
A bus electrode, which is typically formed of metal, on the front substrate causes ambient light to reflect back through the front substrate. This problem deteriorates image quality, including contrast. In order to improve the quality (contrast) of an image, a black electrode or layer can be used to prevent reflection by the bus electrode.
Various processes of forming a black electrode between a transparent electrode and a bus electrode have been suggested. A process of forming a black electrode layer using black metal oxide compounds and their mixture having conductivity and a black pigment consisting mostly of metal oxides having no conductivity has been used. In addition, a process of sequentially forming a black electrode layer and a bus electrode layer and sintering them on a glass substrate at high temperatures so as to reduce the visibility of the electrodes through the rear surface has been used for plasma displays. However, these approaches are costly because of the use of metal oxides, such as RuO2 or ITO in the black electrode layer.
If black metal oxides are used for a photosensitive black electrode material, viscosity is significantly changed over time due to a reaction between the black pigment material and a photosensitive organic material. Thus, undesirably, only a very limited kind of metal oxides may be used as a black pigment.
Additionally, if typical silver powder is used to provide conductivity to a transparent electrode layer, certain problems such as yellowing or reduction of blackness occur.